An apparatus and method for optical data storage and/or retrieval using an optical data storage medium having a spatially-modulated refractive index that can be altered locally with optical methods. Data can be written at a plurality of depths throughout the volume of the medium using a write beam and relatively simple and inexpensive optical components. The write beam stores data locally by physical distortion of the medium at discrete storage locations. The alterations can be detected as variations in the reflectivity of the storage locations using a retrieval beam.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An optical data storage device comprising an optical data storage medium having a format hologram stored within, said format hologram having a periodic, spatially-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg-reflection condition, said optical data storage medium having data stored thereon as localized alterations of said optical data storage medium, said alterations defining a second Bragg-reflection condition.
2. The optical data storage device of claim 1, wherein said periodic, spatially-modulated refractive index varies along a single axis of said holographic storage medium only, said axis defining a depth axis of said holographic storage medium and a plurality of Bragg fringes perpendicular to said depth axis.
3. The optical storage device of claim 2, wherein said localized alterations are written at a plurality of depths of said optical data storage medium.
4. The optical storage device of claim 2, wherein said localized alterations are written at a single depth of said optical data storage medium.
5. The optical storage device of claim 1, wherein said localized alterations in said optical data storage medium are localized expansions of said holographic storage medium.
6. The optical storage device of claim 5, wherein said localized expansions of said optical data storage medium result in localized decreases in the index of refraction.
7. The optical storage device of claim 1, wherein said localized alterations in said optical data storage medium are localized contractions of said optical data storage medium.
8. The optical storage device of claim 7, wherein said localized contractions of said optical data storage medium result in localized increases in the index of refraction.
9. A method for optical data retrieval from an optical storage device, said optical storage device comprising an optical data storage medium having a periodic, spatially-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg-reflection condition, and data stored thereon as localized alterations of said optical data storage medium, said localized alterations defining a second Bragg-reflection condition, said method comprising the steps of: choosing a frequency of a retrieval beam of electromagnetic radiation that is Bragg-matched to said first Bragg reflection condition; focusing a retrieval beam at a plurality of localized storage points within said optical data storage medium to form an output beam; and detecting said output beam to retrieve said stored data.
10. A method for optical data retrieval from an optical storage device, said optical storage device comprising an optical data storage medium having a periodic, spatally-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg-reflection condition, and data stored thereon as localized alterations of said optical data storage medium said alterations defining a second Bragg-reflection condition, said method comprising the steps of: choosing a frequency of a retrieval beam of electromagnetic radiation that is Bragg-matched to said second Bragg reflection condition; focusing a retrieval beam at a plurality of localized storage points within said optical data storage medium to form an output beam; and detecting said output beam to retrieve said stored data.
11. An optical data storage system comprising: an optical data storage medium, said medium having a periodic, spatially-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg-reflection condition; a storage beam of electromagnetic radiation which causes a local alteration of said optical data storage medium when focused onto a localized region within said optical data storage medium, said local alteration defining a second Bragg-reflection condition; and optics means for focusing said storage beam at a plurality of localized storage points within said holographic storage medium.
12. The optical data storage system of claim 11 wherein said storage beam of electromagnetic radiation is of sufficient energy to cause a local alteration of said optical data storage medium.
13. The optical data storage system of claim 11 wherein said storage beam of electromagnetic radiation is of sufficient intensity to cause a local alteration of said optical data storage medium.
14. The optical data storage system of claim 11 wherein said storage beam of electromagnetic radiation is of sufficient duration to cause a local alteration of said optical data storage medium.
15. The optical data storage system of claim 11, wherein said local alterations in said optical data storage medium are inelastic local expansions of said optical data storage medium.
16. The optical data storage system of claim 15, wherein said inelastic local expansions of said optical data storage medium result in local decreases in the index of refraction.
17. The optical data storage system of claim 11, wherein said local alteration in said optical data storage medium are inelastic local contractions of said optical data storage medium.
18. The optical data storage system of claim 17, wherein said local contractions of said optical data storage medium result in local increases in the index of refraction.
19. The optical data storage system of claim 11, wherein said storage beam of electromagnetic radiation is a beam of laser light.
20. The optical data storage system of claim 11, wherein said periodic, spatially-modulated refractive index varies along a single axis of said optical data storage medium only, said axis defining a depth axis of said optical data storage medium and a plurality of Bragg fringes perpendicular to said depth axis.
21. The optical data storage system of claim 20, wherein said localized alterations are written at a plurality of depths within said optical data storage medium.
22. The optical data storage system of claim 20, wherein said optical data storage medium further comprises a format hologram stored within.
23. The optical data storage system of claim 22, wherein said format hologram is a reflection hologram.
24. A method for optical storage of data, said method comprising the steps of: creating an optical data storage medium having a periodic, spatially-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg reflection condition; and altering locally said optical data storage medium at a plurality of localized storage points within said optical data storage medium to result in localized alterations, said localized alterations defining a second Bragg reflection condition.
25. The method of claim 24, wherein said periodic, spatially-modulated refractive index varies along a single axis of said optical data storage medium only, said axis defining a depth axis of said optical data storage medium and a plurality of Bragg fringes perpendicular to said depth axis.
26. The method of claim 24, wherein said localized alterations are written at a plurality of depths within said optical data storage medium.
27. The method of claim 24, wherein said creating step further comprises the sub-step of writing a format hologram in said optical data storage medium.
28. The method of claim 27, wherein said format hologram is a reflection hologram.
29. The method of claim 25, wherein said altering locally step further comprises the steps of: focusing a storage beam of electromagnetic radiation at a plurality of localized storage points within said optical data storage medium; and heating said optical data storage medium to cause a localized inelastic expansion of said holographic storage medium.
30. The method of claim 29, wherein said storage beam of electromagnetic radiation is a beam of laser light.
31. An optical data retrieval system, said system comprising: an optical data storage device comprising: an optical data medium having a periodic, spatially-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg reflection condition; and data stored thereon as localized alterations of said optical data medium, said localized alterations defining a second Bragg reflection condition; a retrieval beam of electromagnetic radiation, having a frequency matched to said first Bragg reflection condition; optics for focusing said retrieval beam onto a plurality of localized storage points within said optical data storage device and forming an output beam; and an optical detector for detecting said output beam to retrieve said stored data.
32. The optical data retrieval system of claim 31, wherein said retrieval beam of electromagnetic radiation is a beam of laser light.
33. An optical data retrieval system, said system comprising: an optical data storage device comprising: an optical data storage medium having a periodic, spatially-modulated refractive index, said periodic, spatially-modulated refractive index defining a first Bragg reflection condition; and data stored thereon as localized alterations of said optical data storage medium, said localized alterations defining a second Bragg reflection condition; a retrieval beam of electromagnetic radiation, having a frequency matched to said second Bragg reflection condition; optics means for focusing said retrieval beam onto a plurality of localized storage points within said optical data storage device and forming an output beam; and an optical detector for detecting said output beam to retrieve said stored data.
34. The optical data retrieval system of claim 33, wherein said retrieval beam of electromagnetic radiation is a beam of laser light.
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July 29, 1999
October 30, 2001
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